Objective lens



EARCH 35o- 471 SR y m50 f i H413@ Jan. 1.1958" J. D HAYES Em' f 2,818,176

4 OBJECTIVE LENS A2M# Filed Jan. 16. 1956 52. u 55 FRONT Q 5 R. I R 4 mm. INVENTOR. v FIG 5 F| s.4 JOHN QgIAYES Y Y LENAM uDsoN.

Homey United States Patent O 2,818,776 OBJECTIVE LENS `lohn D. Hayes, Rochester, and Lena M. Hudson,

Brighton, N. Y., assignors to Bausch & Lomb Optical gonllpany, Rochester, N. Y., a corporation of New Application January 1s, 1956, 'serial No. 559,252

3 Claims. (Cl. 88-57) This invention relates to photographic and similar objective lenses and more particularly it relates to improvements in objectives having four components, one of which may be a compound lens.

This type of objective lens `is typically exemplified in the U. S. Patent 2,487,749, issued November 8, 1949, to C. G. Wynne, and in U. S. Patent 2,672,788, issued March 23, 1954, to T. Brendel which relate to objectives having wide field angles and high relative apertures. Both of the lenses described in the aforesaid patents comprise two negative meniscus components which are concave relative to an intervening diaphragm, said negative components being located between an outer pair of collective lenses and one of the negative components being of compound form.

As a result of recent research work on the aforementioned type of objective by the present inventors, it has been discovered that for best performance, the combined negative powers of the meniscus components and the combinedpowers of the collective lenses should each lie within certain established limits.v Furthermore, the focal length and thickness of the second lens element are of special importance in providing a high degree of correction for the spherical aberration, coma, astigmatism and curvature of field. Further, the interface in the front negative compound lens must be properly formed in order to provide a high degree of chromatic correction.

It is an object of this invention to provide an improved objective lens of the aforementioned type which is well corrected for spherical and chromatic aberrations, coma, astigmatism and curvature of field throughout a'wide lens angle and wherein reduction of the cost and complexity of manufacturing operations may be effected by the use of relatively at lens curvatures, said objectives having a short overall length and a large relative aperture.

These and other objects and advantages will be apparent in the details of construction and in the form and arrangement of the parts of the objective by reference to the specilllication herebelow and the accompanying drawing in whic Fig. 1 is a diagrammatic view of an optical objective incorporating our invention.

Fig. 2 is a table of constructional data relative to said v objective. t v

Fig. 3 is a graph representing the residual tangential and sagittal astigmatism of the objective.

Fig. 4 is a graph representing the spherical aberration of said objective.

A photographic objective constructed according to our invention comprises four optically aligned components, the component nearest to the long conjugate side of the objective being a collective lens designated A, the second component being a negative meniscus compound lens com'- posed of a front double convex element B cementedto a double concave element C and the entire component being airspaced from lens A. Spaced rearwardly thereof is a negative meniscus lens component D which together with the aforementioned compound lens enclose an intervening 1 aperture stop or diaphragm 10, themeniscus lenses being concave thereto. The rear component is a positive or collective lens E spaced rearwardly from the lens D.

According to our invention, an objective having a wide field angle, and high relative aperture and improved image quality as shown in the graphs of Figs. 3 and 4 may be achieved with the use of lenses having relatively at curvatures. In Fig. 3, the letter T indicates the amount of tangential astigmatism of our lens, the letter S indicates the amount of sagittal astigmatism, and the letter D of Fig..4 indicates the amount of spherical aberration. An objective lens having these desirable image forming properties is achieved by making the constructional data conform with the conditions herebelow given. The combined positive power of the two outer collective lenses A and E should be between +1.9P and +2.4P, where P represents the power of the entire objective, while. the combined negative power of the two dispersive meniscus components BC and D should be between 1.5P and -2.1P. The focal length of the B element of the front meniscus component should lie between 50% to 60% of the equivalent focal length of the objective, and its axial thickness t2 should be 70% to 80% of the total thickness trl-t3 of the front meniscus component. The radius R4 of the interface between the B and C lens elements should be 2.0 to 3.0 times the equivalent focal length of the objective and also should be 3.5 to 5.5 times the overall length of the objective. The interface radius R4 is further specified as being greater than three times the sum of the outer radii R3-I-R5 and less than live times said sum as expressed in the mathematical expression,

3 (Rari-R5) R4 5 (RTI-R5) One condition which inuences greatly the curvature of field is the thickness t4 which should be between .14 to .20 times the overall length of the objective.

Constructional data for manufacturing one typical objective lens according to the above specified conditions is given herebelow wherein R1 to R9 inclusive represent the radii of the refractive lens surfaces numbered from the front to the rear, respectively, t1 to t5 inclusive repre-A E. F.=100 f/2.3 F. A.=56

Lens Radll t and S 'ns r R1= 46. 80 A t1= 6. 33 1. 670 47. 2

S1= 1. 0 Rs=f 41. 76 B t2=11. 14 1. 657 50. 9

R4= 226. 0 C ts= 3.16 1. 668 32. 3

Sa== 7. 52 Ro= 25. 27 D l4= 9. 26 1. 649 33.8'

S4= 08 Rg= 985. 84 E fu= 8. 11 1. 620 60. 3

It will be apparent'to those skilled in this art that other typical forms of photographic objectives may be constructed within the specifications and conditions set forth in the above description and changes and substitutions may be made therein without departing from the spirit of facin a diaphragm located therebetween, the last-men- *tione componn'fs'eing situated between two outer comfront side of said diaphragm being a compound lens having on its front side a double convex element which is ce-v mented to a double concave element thus providing an interface therebetween which is convex toward said dia- Y ponents of postive power, the component adjacent to the y phragm, said interface having a radius of curvature that is 2.0 to 3.0 times longer than the equivalent focal length of said objective and is 3.5 to 5.5 times longer than the overall length of said objective, the component adjacent to the rear side of said diaphragm being a single lens, the combined negative power of the innermost components being between 1.5P and 2.1P where P represents the power of the entire objective and the combined positive power of the outermost components being between +1.9P and +2.4P, and the axial thickness of the rearmost negative meniscus lens being between 14% and 20% of the overall length of said objective. y

2. A photographic objective or the like having a relative aperture at least as large as f/2.3 which is corrected for spherical and chromatic aberrations, coma, astigmatism and curvature of iield comprising four air spaced lens components in optical alignment with each other, the two innermost of said components being negative meniscus lenses having concave sides facing each other and having a diaphragm located between said sides, two positive components between which said negative meniscus lenses are situated, the negative component adjacent to the front side of said diaphragm being formed from a double convex front element which has a focal length between 50% and 60% of the equivalent focal length of the objective and the thickness t2 of the double convex element being .7 to .9 of the total axial thickness of the compound component and the difference of refractive index between the convex and the concave elements being substantially .011,

the radii R1 to R9 of the successive refractive surfaces of the lens elements numbering from the front being related to the equivalent focal length F of the objective according to the mathematical expression 3.v A photographic objective having a wide field angle and a relative aperture at least as large as f/ 2.3 which is corrected for spherical and chromatic aberrations, coma,

astigmatism and curvature of lield comprising a pair of concavo-convex dispersive lenses having their concave sides facing each other and facing an interposed aperture stop, a pair of collective lenses between which said dispersive lenses are positioned in air spaced and optically aligned relation, the foremost of said dispersive lenses being formed from a front double convex element which is cemented to a rear double concave element, one form of said objective being constructed according to the numerical data given herebelow wherein R1 to R9 are the radii of the refractive surfaces in their order of occurrence from front to rear, t1 to t5 are the thicknesses of the various lens elements A to E respectively, S1 to S4 are the separations of said elements A to E respectively, nn denotes the refractive indices for'the D line of the spectrum and v denotes the Abbe numbers of said elements.

Eqluivalent focal length=100 ative aperture =f/2.3 Field angle=56 Thick- Lens Radli nessest and n v spaces S A R=+ 46'80 i1= 3.33 1.670 47.2

Ri=+13a3s Sif- 1.0 Ri=+ 41.76 1 B 1i= 11.14 1. 657 50. 9

rtw-228.0 o 1|= 3.13 1. 65s 32.3

v S2=l 9.30 S1= 7.52 R= 25.27 D ti- 9.26 1.649 33.8

- S4=- .08 Ri=+9s5-a4 E ti= 8.11 1. 520 60.3

References Cited in the lile of this patent UNITED STATES PATENTS y 2,117,252 L'ee May 10, 1938 2,171,640 Berck Sep. 5, 1939 2,391,209. Warmisham Dec. 18, 1945 2,487,749 Wynne Nov. 8, 1949 2,672,788 Brendel Mar. 23, 1954 FOREIGN PATENTS j 575,076 Great Britain Feb. l, 1946 

